The research of phase evaporation in oil-based mud is an important task and has practical significance for specialists engaged in engineering support of drilling muds. The main aim of the study: development method for studying the evaporation oil-based mud components, to study the kinetics of evaporation of hydrocarbon and water phases, and the degree of change in technological characteristics of oil-based mud, to obtain the algorithm of restoring the original concentrations of emulsion. The methods used in the study: the authorsґ express method of researching evaporation of oil-based mud components, retort analysis, electrical stability analysis and methods for determining technological characteristics of drilling fluids by API (American Petroleum Institute) standards. The results. The authors have developed the express method of researching evaporation of the oil-based mud components. It was ascertained that significant evaporation of water and hydrocarbon phases occurs at 60 °C and the process is divided into two stages: active evaporation, significant reduction in mud weight due to the water phase evaporation (the first 4 hours), slow evaporation, alignment of the ratio of the volume of the evaporated phases (4-12 hours). It was ascertained that the emulsion rheological parameters grow intensively due to increased concentration of the solid phase and density at water and mineral oil evaporation. The authors introduced the specific volume of evaporation, depending on time, which allows calculating the amount of hydrocarbon and water needed to restore the initial concentration. The authors developed the algorithm of recovering initial concentrations of the oil-based mud components. Its application can greatly simplify the control over the washing liquid quality, increase the efficiency of the most modern oil-based muds when drilling with high downhole temperatures.